1. Field of the Invention
The present invention relates to a semiconductor device including a large scale integrated circuit and a method for manufacturing the semiconductor device. More particularly, the present invention relates to a semiconductor device and a manufacturing method thereof characterized in a contact portion between a substrate and a metallic wiring layer and in formation of a gate electrode as a silicide.
2. Description of the Related Art
As a semiconductor integrated circuit is large-sized and wiring patterns of this semiconductor integrated circuit are finely formed, a method for forming a silicide is used to reduce contact resistances between a substrate and metallic wirings and resistances of the wirings and a gate electrode so as to operate the semiconductor integrated circuit at a high speed.
In silicide formation, a high melting point metallic polycrystal film of titanium, etc. is formed on an exposed portion of a silicon substrate and a polycrystal silicon wiring by using a sputtering method. This polycrystal film is rapidly processed thermally in a nitrogen atmosphere. Thus, portions of the metallic polycrystal film coming in contact with the exposed portion of the silicon substrate and the polycrystal silicon film are formed as a silicide. FIG. 1a shows general silicide forming processes. In FIG. 1a, a polycrystal titanium film 4 is formed on a silicon substrate 2 by a sputtering method. A normal sputtering method for forming the titanium film 4 is a DC sputtering method. In the DC sputtering method, a target voltage is set to -400 to -600 V and a substrate voltage is set to -10 to -100 V with respect to a film forming chamber having a ground potential. A sputtering atmosphere is formed by argon (Ar) gas. As shown by process (a1) of FIG. 1a, a crystal grain boundary 6 exists in the polycrystal titanium film 4. A silicide is formed by processing this polycrystal titanium film 4 rapidly and thermally. In this case, a silicide is preferentially formed from an unstable portion of the grain boundary 6 so that a silicide film 8 is ununiformly formed as shown by process (a2) of FIG. 1a. In a serious case, in the rapid thermal processing for the silicide film formation, a discontinuous silicide layer locally having no silicide layer is formed in a portion in which the silicide film should be formed on a diffusive layer and a gate electrode. The crystal grain boundary of the silicide film is formed in a wide range of a size from several hundred nm to several .mu.m.
When the discontinuous silicide film is formed on surfaces of the diffusive layer and the gate electrode, sheet resistance of the silicide film is increased. When the crystal grain boundary is formed in the wide range from several hundred nm to several .mu.m, sheet resistance of a gate electrode becomes ununiform when the gate electrode is formed as an electrode having a narrow width such as a width equal to or smaller than 1 .mu.m.
In the ununiform silicide film, agglomeration is caused in a heat treatment process at a subsequent forming time of a layer-insulation film, etc. Therefore, one method for preventing agglomeration of the silicide film is proposed in IEEE, 1990, VMIC Conf., pp. 310-316, etc. In this method, a polycrystal titanium film is formed on an exposed portion of a silicon substrate and a polycrystal silicon film. Thereafter, nitrogen ions are implanted into the polycrystal titanium film. Then, the polycrystal titanium film is thermally processed to form a silicide.
However, in this method, an operation rate of the manufacturing device is reduced by adding an ion implanting process.